Separator

ABSTRACT

A separator has a first inlet arranged to receive a fluid stream, and first and second separation stages coupled together in series; A pump coupled to the second separation stage generates an area of reduced pressure to draw the fluid stream through the first and second separation stages. One of the stages includes a variable impactor separator comprising a first chamber arranged to receive the fluid stream, and a second chamber coupled to the first chamber through an aperture to accelerate the first fluid stream. The stream is incident upon an impaction surface to separate contaminants from the fluid stream. An actuator adjusts the open area of the aperture according to a pressure differential between fluid pressure in the first chamber and a reference fluid pressure in a third chamber. The other of the separation stages is a second variable impactor separator or a filter media.

CROSS REFERENCE TO RELATED APPLICATIONS

The within application is a continuation of International ApplicationNo. PCT/GB2012/051729, filed Jul. 19, 2012, and which designated theUnited States; and which claims priority to Great Britain ApplicationNo. 113072.1, filed Jul. 29, 2011, the disclosures of which areexpressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a separator. In particular, the presentinvention relates to a separator for separating particulate, liquid andaerosol contaminants from a fluid stream. Certain embodiments of thepresent invention relate to a separator for separating particulate,liquid and aerosol contaminants from a blow-by gas stream within areciprocating engine. Separators in accordance with particularembodiments of the present invention incorporate mechanisms forregulating the pressure within a crankcase ventilation system.Embodiments of the present invention provide a pump assisted integralseparator and regulator suitable for use in a crankcase ventilationsystem.

Blow-by gas within a reciprocating engine is generated as a by-productof the combustion process. During combustion, some of the mixture ofcombustion gases escape past piston rings or other seals and enter theengine crankcase outside of the pistons. The term “blow-by” refers tothe fact that the gas has blown past the piston seals. The flow level ofblow-by gas is dependent upon several factors, for example the enginedisplacement, the effectiveness of the piston cylinder seals and thepower output of the engine. Blow-by gas typically has the followingcomponents: oil (as both a liquid and an aerosol, with aerosol dropletsin the range 0.1 μm to 10 μm), soot particles, nitrous oxides (NOx),hydrocarbons (both gaseous hydrocarbons and gaseous aldehydes), carbonmonoxide, carbon dioxide, oxygen, water and other gaseous aircomponents.

If blow-by gas is retained within a crankcase with no outlet thepressure within the crankcase rises until the pressure is relieved byleakage of crankcase oil elsewhere within the engine, for example at thecrankcase seals, dipstick seals or turbocharger seals. Such a leak mayresult in damage to the engine.

In order to prevent such damage, and excessive loss of oil, it is knownto provide an outlet valve that allows the blow-by gas to be vented tothe atmosphere. However, with increasing environmental awarenessgenerally, and within the motor industry in particular, it is becomingunacceptable to allow blow-by gas to be vented to atmosphere due to thedischarge of oil and other contaminants from within the crankcase.Furthermore, such venting increases the speed at which crankcase oil isconsumed.

Consequently, it is known to filter the blow-by gas. The filteredblow-by gas may then be vented to the atmosphere as before (in an openloop system). Separated oil is returned to the sump via a drain hose.The blow-by gas may pass through a filtering medium or another knownform of gas contaminant separator to remove oil, soot and othercontaminants to protect engine components from fouling and any resultantreduction in performance or failure of a component. In order to avoidunacceptably high engine crankcase pressures, such a separator must nothave a flow pressure differential higher than an allowable limit whichis defined by the engine manufacturer in order to avoid oil leakage fromthe engine crankcase and other seals. Typically an upper limit ofbetween 5 mbar and 50 mbar is set.

By returning the cleaned blow-by gas to the air intake of an engine (toform a closed loop system) it is ensured that no oil aerosols remainingafter separation are vented to atmosphere. For such systems (known asClosed Crankcase Ventilation systems) the small vacuum created by theengine air intake results in the requirement for a separate pressureregulator to prevent negative pressures being translated to engine atsome transient speed and load conditions.

Where cleaned blow-by gas is returned to the air intake of an engine viaa turbo-charger system it is necessary to comply with the specificationsfor how clean the air must be from the turbo-charger manufacturer. Forinstance, a typical maximum oil contamination rate for turbo-chargers is0.2 g per hour. This requirement can further increase the requiredseparation efficiency.

The maximum gravimetric efficiency of known separators having a pressuredifferential within the range defined by either an open or a closedcrankcase ventilation system have been measured and are known by thosein the industry. Generally 70%-80% of oil aerosols can be removed bymass. The application of two separators in series, each utilising aportion of the available pressure differential has been found to yieldno significant improvement in overall efficiency.

There is an increasing demand for higher separation efficiency in bothopen and closed loop systems. For instance, an overall oil separationefficiency of greater than 98% measured by mass (gravimetric) forparticles collected using an absolute measurement filter is required bymany engine manufacturers. Utilising state of the art equipment, thefractional efficiency (that is, the separation performance of the deviceat any given particle size) can be measured for particle sizes largerthan around 0.03 μm. The particle challenge characteristics of theengine (that is, the fractional makeup of the contaminants) cansimilarly be measured. In some cases an efficiency requirement is givenfor specific particle sizes as small as 0.2 μm, which may be as high as85%. Furthermore, emissions legislation in Europe and the US areincrementally increasing the required separation efficiency such that itwill soon be necessary to achieve 99% gravimetric separationefficiencies.

Separation using filter mediums is undesirable as such filters have afinite lifespan before they become clogged and must be replaced. Enginemanufacturers and end users in general prefer to only use enginecomponents that can remain in place for the life of the engine. Whilefit for life separators are known, typically only powered centrifugalseparators and electrostatic precipitators have hitherto been able toachieve the required levels of separation efficiency. Such separatorsare costly to manufacture, consume electrical power, or have movingparts which may be prone to wear. Low cost, fit for life impactorseparators (where separation occurs as a contaminated gas stream isincident upon an impactor plate transverse to the gas flow) are notusually able to achieve the required separation efficiency. Impactorseparators are also referred to in the art as inertial gas-liquidimpactor separators. It is known to use inertial gas-liquid impactorseparators in both open and closed crankcase ventilation systems.Contaminants are removed from the fluid stream by accelerating the fluidto a high velocity through a slit, nozzle or other orifice and directingthe fluid stream against an impactor plate to cause a sharp directionalchange.

WO-2009/037496-A2 in the name Parker Hannifin (UK) Ltd discloses aseparator for separating contaminants from a fluid stream. The separatorcomprises: a chamber, a first inlet for receiving a first fluid stream,the first inlet having a convergent nozzle for accelerating the firstfluid stream and a second inlet for receiving a second fluid streamincluding entrained contaminants, for instance blow-by gas. The secondinlet is arranged relative to the first inlet such that the first fluidstream can entrain and accelerate the second fluid stream forming acombined fluid stream within the chamber. A surface is coupled to thechamber and arranged such that the surface can cause a deviation in thecourse of the combined fluid stream incident upon it such thatcontaminants are separated from the combined fluid stream.

According to this known form of separator, contaminants can be removedfrom a fluid stream to a high level of efficiency without the need fordriven or moving parts. The separator is suitable for separatingcontaminants from a gas stream such as a blow-by gas stream derived froman internal combustion engine. The first fluid stream may be derivedfrom a turbo compressor or other source of compressed air within avehicle engine and serves to draw the blow-by gas from the crankcase ofan engine. The first fluid stream forms an area of reduced pressure inthe chamber which draws in the blow-by gas. Such a separator may be afit for life separator owing to the absence of moving parts that mayfail or filter mediums that would be prone to clogging and requirefrequent replacement.

For separators having an impaction surface arranged to cause separationby deflecting the fluid stream, the separation efficiency can beincreased by providing a nozzle through which the fluid stream passes.The nozzle causes the fluid stream to be accelerated such that the fluidstream is incident upon the impaction surface at a higher velocity. Itis desirable to apply a nozzle with the smallest possible crosssectional area in order to achieve the highest velocity and separationefficiencies. An undesirable consequence of this is that there is ahigher pressure drop created across the separator. In order to preventthe crankcase pressure increasing to unacceptable levels, the minimumsize of the nozzle and consequently the performance of the separator islimited. To control crankcase pressure within acceptable limits apressure regulator must also be added either upstream or downstream ofthe separator.

Such inertial separators as described above, having fixed sectionnozzles produce an air-stream having a uniform velocity across theimpactor face. Due to the difference in inertia of different sizedparticles a characteristic fractional separation efficiency profileresults with the smallest particles having significantly lower chancesof successful separation compared to larger and heavier particles.

SUMMARY OF THE INVENTION

It is an object of embodiments of the present invention to obviate ormitigate one or more of the problems associated with the prior art,whether identified herein or elsewhere. Specifically, it is an object ofembodiments of the present invention to provide further improvements inthe efficiency of crankcase ventilation systems, in particular, fit forlife closed crankcase ventilation systems (CCV systems). Certainembodiments of the present invention are not dependent upon electricalpower, or complex rotating parts. It is a further object of embodimentsof the present invention to provide a high efficiency separator that canprevent the fluid inlet pressure rising to unacceptable levels.

According to a first aspect of the present invention there is provided aseparator for separating contaminants from a fluid stream, the separatorcomprising: a first inlet arranged to receive a first fluid streamincluding entrained contaminants; first and second separation stagescoupled together in series and coupled to the first inlet to receive thefirst fluid stream from the first inlet and each arranged to separatecontaminants from the first fluid stream; and a pump coupled to thesecond separation stage and arranged to generate an area of reducedpressure to draw the first fluid stream through the first and secondseparation stages; wherein one of the separation stages comprises avariable impactor separator comprising: a first chamber arranged toreceive the first fluid stream; a second chamber coupled to the firstchamber through at least one aperture arranged such that the first fluidstream is accelerated through the aperture and is incident upon animpaction surface such that contaminants are separated from the firstfluid stream; and an actuator arranged to adjust the open area of theaperture, each aperture or the group of apertures according to apressure differential between fluid pressure in the first chamber and areference fluid pressure in a third chamber; and wherein the other ofthe separation stages comprises one of a second variable impactorseparator and a filter media.

A feature of the present invention is that the pump generates a regionof reduced pressure downstream of the impaction surface which allows fora high pressure differential to be maintained across the separatorstages without causing the inlet pressure to rise to unacceptablelevels. Furthermore, the variable impactor separator or at least one ofthe variable impactor separators ensures that the inlet pressure ismaintained at a predetermined level relative to the pressure reference.Preferably the pressure reference is the ambient environment, allowingthe crankcase pressure to be closely controlled at or around the ambientenvironmental pressure, reducing the pressure on engine seals.

Separators in accordance with embodiments of the present invention areable to achieve significantly higher rates of both gravimetric andfractional separation efficiency by dividing the available pressure dropprovided by the pump across two or more separation stages compared withthe performance of a single stage separator utilising the same pressuredrop. This significant result is not achievable without the benefit ofan external energy source in the form of a pump. At the same time thevariable impactor or each variable impactor separation stage allows theseparation efficiency to be maximised while providing effective pressureregulation across the separator to prevent the crankcase pressurefalling below or exceeding predetermined limits. The or each variableimpactor separator additionally controls the open area of the apertureaccording to the available pump pressure. This control over the openarea of the aperture reduces or fully eliminates the effect of pumpsurge and high and low pressure hunting, which commonly occur withunregulated or poorly regulated pumped separators.

For the variable impactor separator or at least one of the variableimpactor separators the impaction surface may be within the secondchamber and is arranged to deflect the first fluid stream after thefirst fluid stream enters the second chamber such that contaminants areseparated from the first fluid stream.

For the variable impactor separator or at least one of the variableimpactor separators the shape of the aperture may be chosen such thatthe rate of change of the open area of the aperture has a non-linearresponse to a change in the pressure differential between the first andthird chambers.

For the variable impactor separator or at least one of the variableimpactor separators the actuator may comprise a diaphragm separating thefirst chamber from the third chamber.

For the variable impactor separator or at least one of the variableimpactor separators the first chamber may be defined by an inner tubearranged to receive the first fluid stream at a first end of the innertube and the second chamber is defined by an outer tube surrounding thefirst chamber, the second end of the inner tube being closed by thediaphragm.

For the variable impactor separator or at least one of the variableimpactor separators the diaphragm may be arranged to move along alongitudinal axis of the tubes in response to a change in the pressuredifferential between the first chamber and the pressure reference.

For the variable impactor separator or at least one of the variableimpactor separators the aperture may comprise a slot through the innertube wall and the diaphragm may further comprise a flexible portionarranged to progressively cover and uncover the slot to vary the opensize of the aperture as the diaphragm moves. In alternative embodimentsthe slot may be replaced by a series of discrete slots, apertures orother openings between the chambers.

The separator may further comprise a drain arranged to allow liquidcontaminants to drain from the separator.

The first separation stage may comprise a variable impactor separatorand the second separation stage comprises a filter media coupled betweenthe first separation stage and the pump, the filter media comprising apass through filter media arranged to trap a portion of contaminantsentrained in the first fluid stream.

The pump may comprise a fourth chamber having a second inlet forreceiving a second fluid stream into the fourth chamber, the secondinlet including a convergent nozzle for accelerating the second fluidstream, and a third inlet for receiving the first fluid stream, thethird inlet being arranged relative to the second inlet such that thesecond fluid stream can entrain and accelerate the first fluid stream.Alternatively, the pump is electrically or hydraulically driven.

The separator may further comprise a cyclonic separator coupled betweenthe first inlet and the first separation stage, the cyclonic separatorbeing arranged to cause fluid received from the first inlet toaccelerate through a spiral course to separate contaminants from thefirst fluid stream.

The first separation stage may comprise a variable impactor separatorand an inner tube defining the first chamber of the variable impactorseparator extends downwards into the cyclonic separator to form thevortex finder of the cyclonic separator.

According to a second aspect of the present invention there is provideda crankcase ventilation system comprising: a blow-by gas duct arrangedto receive blow-by gas from a crankcase; and a separator according toany one of the preceding claims, wherein the first inlet is coupled tothe blow-by gas duct.

The pump may be arranged to be coupled to an engine air inlet system, toa vehicle exhaust system or to discharge gases to the ambientenvironment.

According to a third aspect of the present invention there is providedan internal combustion engine comprising a crankcase ventilation systemas described above, wherein the second inlet is arranged to receive apressurised gas stream derived from a turbocharger and the separator isoperable to separate crankcase oil from the blow-by gas.

In a further embodiment of the present invention there is provided aseparator for separating contaminants from a fluid stream, the separatorcomprising: a first inlet arranged to receive a first fluid streamincluding entrained contaminants; first and second separation stagescoupled together in series and coupled to the first inlet to receive thefirst fluid stream from the first inlet and each arranged to separatecontaminants from the first fluid stream; and a pump coupled to thesecond separation stage and arranged to generate an area of reducedpressure to draw the first fluid stream through the first and secondseparation stages; wherein one of the separation stages comprises avariable impactor separator comprising: a first chamber arranged toreceive the first fluid stream; a second chamber coupled to the firstchamber through an aperture arranged such that the first fluid stream isaccelerated through the aperture and is incident upon an impactionsurface such that contaminants are separated from the first fluidstream; and an actuator arranged to adjust the open area of the apertureaccording to a pressure differential between fluid pressure in the firstchamber and a reference fluid pressure in a third chamber; and whereinthe other of the separation stages comprises one of a second variableimpactor separator, a filter media and a cyclonic filter coupled betweenthe first inlet and the variable impactor separator.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates an engine system including a closedcrankcase ventilation system;

FIG. 2 illustrates in a cross sectional view a CCV system including animpactor separator arranged to have a variable response to changingcrankcase pressure;

FIG. 3 is an enlarged cross sectional view of the CCV system impactorseparator of FIG. 2;

FIG. 4 is a perspective view of the impactor tube of FIG. 2;

FIG. 5 is a cross sectional view of an alternative CCV system impactorseparator;

FIG. 6 is an enlarged cross sectional view of a diaphragm forming partof the CCV system impactor separator of FIG. 5 in a closed position;

FIG. 7 is an enlarged cross sectional view of a diaphragm forming partof the CCV system impactor separator of FIG. 5 in an open position;

FIG. 8 illustrates in a cross sectional view a CCV separator inaccordance with a first embodiment of the present invention includingfirst and second stage impactor separators each of which is arranged tohave a variable response to changing crankcase pressure;

FIG. 9 illustrates in a cross sectional view a CCV separator inaccordance with a second embodiment of the present invention including afirst stage impactor separator arranged to have a variable response tochanging crankcase pressure and a second stage media separator;

FIG. 10 illustrates the variation of overall gravimetric separationefficiency for multi-stage separators comprising two, three or fourimpactor separators with the gravimetric separation efficiency of eachimpactor separator stage;

FIG. 11 illustrates the aerosol mass fraction challenge for blow-by gasderived from a 2010 diesel engine between 0.02 μm and 8 μm;

FIG. 12 illustrates the interdependence between pressure differentialand fractional separation efficiency for a single stage variableimpactor separator;

FIG. 13 illustrates the fractional separation efficiency of 120 mBar and60 mBar variable impactor separators, and the target fractionalseparation efficiency of each of two 60 mBar variable impactorseparators in a two stage separator;

FIG. 14 illustrates the fractional separation efficiency of 120 mBar and60 mBar variable impactor separators, and a two stage separatorcomprising two 60 mBar variable impactor separators coupled together inseries;

FIG. 15 illustrates the fractional separation efficiency of 100 mBar and50 mBar variable impactor separators, and a two stage separatorcomprising two 50 mBar variable impactor separators coupled together inseries; and

FIG. 16 illustrates the fractional separation efficiency of an unpoweredvariable impactor separator, a pump assisted variable impactorseparator, a low density filter media and the combination of a pumpassisted variable impactor separator and a low density filter mediacoupled together in series.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The conventional arrangement of an engine blow-by gas/oil separatorreturning cleaned gas to an engine air intake is commonly referred to asa closed crankcase ventilation system (CCV system). Known CCV systemsrequire the use of a crankcase pressure regulator in order to ensurethat an excessive proportion of the vacuum generated by the engine airintake is not translated via the CCV separator to the engine crankcase.

Referring to FIG. 1, this illustrates the arrangement of a conventionalCCV system 2 coupled to a diesel engine 4. Blow-by gas from the enginecrankcase passes to the CCV system 2 along inlet duct 6. The CCV system2 comprises a regulator 8 coupled to the inlet duct 6 and a contaminantseparator 10 in series. The regulator 8 and separator 10 are showncombined in FIG. 1.

A pump 12 may optionally be provided within the CCV system (notseparately visible in FIG. 1) to increase the pressure drop across theseparator 10, thereby increasing the filtering efficiency. Cleanedblow-by gas exits the CCV system through gas outlet 14 and is returnedto the engine air intake system. Specifically, the engine air intakesystem draws in air from outside of the vehicle through an inlet 16, theair then passing through an inlet air filter and silencer 18, acompressor 20 driven by a turbo charger 22 (in turn driven by the engineexhaust 24) and an after cooler 26 to cool the compressed air before itis supplied to the engine 4. The cleaned blow-by gas passes from the gasoutlet 14 to the compressor 20. Oil and other contaminants separatedfrom the blow-by gas are returned to the engine crankcase through oildrain 28.

In the system of FIG. 1 a portion of the vacuum generated between theturbocharger 22 and the air filter 18 is lost over the blow-by separator10. The regulator 8 controls any remaining vacuum that would otherwisebe exposed to the engine crankcase. It can be seen that the total airflow drawn by the turbo compressor 22 is not necessarily restricted bythe closing of the regulator, since the difference can be drawn via theengine air filter 18.

Referring now to FIG. 2, this illustrates a cross sectional view of aCCV system for separating liquid, aerosol and particulate contaminantsfrom a blow-by gas stream. The separator comprises a variable impactorseparator which is arranged to automatically adjust the size of anaperture through which the blow-by gases to optimise separationefficiency and to provide a degree of integral pressure regulation toprevent excessive pressure variation within the crankcase as the vacuumdeveloped by a pump varies over time. The respective portions comprisinga separate pressure regulator 8, a separator 10 and a pump 12 areindicated.

The regulator 8 comprises a floating diaphragm 30 which is arranged toopen or close to restrict blow-by gas flow and regulate the crankcasepressure as required. Blow-by gas enters a first regulator chamber 32through the CCV gas inlet 6. Chamber 32 is at substantially the samepressure as the engine crankcase. The diaphragm 30 at least partiallyoccludes the gap between the first chamber 32 and a second chamber 34(in turn coupled to the separator 10). A first side of diaphragm 30 isexposed to the blow-by gas in chamber 32. A second side of the diaphragm30 is exposed to an ambient gas pressure within a chamber 36, which hasan opening to the ambient environment. Alternatively, the third chamber36 may be coupled to a separate pressure reference.

Movement of the diaphragm 30 is controlled by first and second springs38, 40. Spring 38 is positioned within the second chamber and resistsmovement of the diaphragm 30 to close the gap between the first andsecond chambers 32, 34. Spring 40 is positioned within the third chamber36 and resists movement of the diaphragm 30 to open the gap between thefirst and second chambers 32, 34. Adjustment of the response of springs38, 40 and adjustment of the relative sizes of the first and secondsides of the diaphragm 30 acted upon by the blow-by gas and the ambientgas pressure can be used to control the rate and extent of movement ofthe diaphragm 30.

Integral pump 12 improves the separation performance of the CCV system 2by generating a larger vacuum to draw the blow-by gas through theseparator 10 than the vacuum available from the compressor 20. Thepressure in the first chamber 32 is regulated to the desired crankcasepressure by specification of the pump to generate the required vacuum,specifying appropriate pressure regulation spring forces withinregulator 8 and by specifying the pressure response of the separator 10,as described in greater detail below. The pressure in the second chamber34 is defined by the variable pressure loss across the separator(according to the pressure response of the separator 10) and the vacuumgenerated by the pump 12. The vacuum generated is determined accordingto the operating point along the chosen pump's flow versus pressureperformance curve.

It will be appreciated that for a pumped CCV separator system the flowthrough the pump can be entirely restricted by the position of theregulator diaphragm. For the regulator illustrated in FIG. 2, if thediaphragm 30 comes into contact with the end of tubular wall 42separating the first and second chambers 32, 34 then gas flow betweenthe first and second chambers is interrupted. The effect upon the pump12 is similar to the phenomena of pump surge in which an unregulateddisplacement pump can give rise to spikes in the output pressure.Restricted flow resulting from a mostly or fully closed regulator movesthe pump operating point to a corresponding low flow and high vacuumposition. The increased vacuum generated in the second chamber 34further increases the force acting on the vacuum regulation springs 38,40 and the flow of blow-by gas is restricted yet further. Only greaterforce acting upon the diaphragm 30 generated by a build up of positivepressure in the engine crankcase can open the regulator again. Asdiscussed above, excessive pressure build up in a crankcase can resultin damage to the crankcase and escape of oil. A closed loop controlcycle of high and low pressure hunting results between the regulator andthe pump which cannot be controlled with a conventional linear responseregulator.

The problems of high and low pressure hunting for pumped CCV systems mayalso be experienced within other forms of crankcase ventilation systems.Specifically, pressure hunting may occur in open crankcase ventilationsystems, non-pumped closed crankcase ventilation systems and exhaustpumped ventilation systems. More generally, the problems discussed aboveassociated with conventional regulators may occur in any system whichincludes a pressure regulator.

An improved regulator which addresses the problems of high and lowpressure hunting and pump surge is the subject of a separator patentapplication published as WO-2011/070341-A1 in the name Parker Hannifin(UK) Ltd. In accordance with certain embodiments of the presentinvention, the CCV system may incorporate an impactor separator whichimplements a similar form of pressure regulation to that disclosed inWO-2011/070341-A1.

Pump 12 serves to generate a region of low gas pressure in order to drawcontaminated blow-by gases through separator 10. The pump 12 inaccordance with certain embodiments of the present invention can beconsidered to be a type of jet pump. Similar jet pumps in combinationwith separators are described in WO-2009/037496-A2. A first inlet 50 tothe pump 12 receives a source of pressurised gas, referred to herein asboost gas. The boost gas may be provided by the turbo charger 22 or anyother source of pressurised gas such as exhaust gas. The boost gas neednot be at a high velocity on entering the boost gas inlet. The boost gascould be static, though under pressure. Optionally, the boost gas couldbe obtained from the exhaust or the turbocharger and stored in aseparate holding chamber or collector prior to being passed to the boostgas inlet.

Boost gas enters the pump via boost gas inlet 50. When used on aturbocharged engine the boost gas may be a derived from a source ofpressurised gas such as the intake manifold. Alternatively, thepressurised gas could be derived directly from the turbocharger, howeverit is preferable to derive the air from the intake manifold as at thisstage the turbocharger gas has passed through a heat exchanger(alternatively referred to as an intercooler) so that it is cooled fromapproximately 180-200° C. to 50-60° C. Using cooler boost gas allows theseparator to be formed from lower cost materials which do not need to beresistant to such high temperatures. Alternatively, exhaust gas derivedfrom before or after the turbocharger may be used as the boost gas. Theboost gas is typically between 1 Bar absolute pressure and 4 Barabsolute pressure (up to 3 Bar above atmospheric pressure).

The boost gas passes through nozzle 52, which accelerates the boost gas(and causes a consequent reduction in pressure). The nozzle 52 is formedas a convergent nozzle. In particular, the nozzle may be aconvergent-divergent nozzle, such as a de-Lavaal nozzle, which is wellknown in the art. Other suitable nozzle shapes are known, including anynozzle having a restricted central portion. The boost gas is acceleratedto a high velocity, for instance between 100-500 m·s⁻¹, with the boostgas typically exceeding mach 1 at least in the region of nozzle 52. Aconvergent nozzle advantageously accelerates the boost gas to very highspeeds, which consequently entrains the blow-by gas and accelerates theblow-by gas to high speeds. The nozzle is arranged to generate a regionof reduced pressure to draw in the blow-by gas.

The resultant high speed boost gas jet passes into chamber 54. The highvelocity boost gas jet causes a region of reduced pressure within thechamber 54 in the vicinity of the nozzle 52. Pressure is reduced by upto 300 mBar relative to external atmospheric pressure. This magnitude ofavailable pressure reduction is required to accommodate a significantincrease in blow-by gas flow rates as the engine wears relative to theperformance of a new engine. As components of the engine wear, inparticular the piston seals, increasing the rate of production ofblow-by gas, the variable impactor separator increases the open area ofthe aperture to allow a larger volume of blow-by gas to pass throughthereby maintaining the pressure within the crankcase to withinpredetermined limits. The effect is that for a worn engine the pressurereduction within chamber 54 relative to the external atmosphericpressure may be lowered to around 150 mBar. This reduction in pressureallows cleaned blow-by gas from the separator 10 to be drawn intochamber 54. The passage of the blow-by gas from regulator 8 throughseparator 10 is described below. Blow-by gas is sucked into chamber 54.The blow-by gas flow is entrained and accelerated by the boost gas,intermixing with the boost gas and accelerating to approach the speed ofthe boost gas.

The boost gas nozzle 52 and the annular blow-by gas inlet 54 aregenerally constructed in the form of a jet pump, as is known in the art.The combined gas stream passes into a diffuser tube 110. In order toachieve satisfactory entrainment and acceleration of the blow-by gas,preferably the diameter of the diffuser tube 110 should be between 2 to5 times greater, preferably 3 to 4 times greater, than the criticaldiameter (typically, the smallest diameter) of boost gas nozzle 52. Theposition of the critical diameter (alternatively referred to as thethroat of the nozzle) may vary from the narrowest point of the nozzledue to aerodynamic effects, as is known in the art of nozzle design.

The diffuser tube is generally formed as a cylinder; however the sidewalls are not necessarily straight for the whole of their length. Theside walls may taper outwardly towards the end of the tube remote fromnozzle 52. This tapering assists in controlling the direction of flowand mixing of the combined gas flow.

The contaminated blow-by gas is actively drawn out of the crankcase andthrough the separator allowing for control of the crankcase pressure.The pressure within the crankcase is typically controlled to within+/−50 mBar relative to external atmospheric pressure, with the pressuredifferential to atmospheric pressure controlled by the regulator 8 asdescribed above. The pressure drop from the crankcase pressure inchamber 32 to the low pressure in chamber 54 allows for higherefficiency separation within separator 10, as described below.

It will be appreciated that although the primary form of pump describedin the present specification is a jet pump as shown in FIG. 2, otherknown forms of pump such as electric pumps may be used in order toachieve the required pressure drop across separator 10. The pressuredrop across the separator 10 generated by the pump 12 overcomes the highpressure differential of the separator 10 without causing an excessivelyhigh crankcase pressure. That is, because of the reduction in pressurecaused by the pump 12, the blow-by gas may be drawn through a smallerimpaction gap causing more efficient separation.

After the blow-by gas passes through regulator 8 into chamber 34, thegas is drawn into the separator inlet tube 60 via a cyclonicpre-separator 61 generally along the path indicated by arrow 62. Thecyclonic pre-separator 61 is generally conical and the blow-by gasenters via an inlet from the regulator 8 towards one side of thecyclone. The separator inlet tube 60 projects downwards into the cyclone61 and serves as the vortex finder for the cyclone. The cyclonic airflowcauses contaminants to be impacted against the walls of the cyclone 61and a proportion of the contaminants is separated from the blow-by gasand flows downwards towards oil drain 28 while the blow-by gas is drawnup through the inlet tube 60.

The separator inlet tube 60 is partially closed at its upper end bydiaphragm 64. The blow-by gas then passes through one or more slots 66and is incident upon an annular impaction surface 68. Oil and othercontaminants separated from the blow-by gas at impaction surface 68 flowunder gravity to oil sump 70 surrounding the separator inlet tube 60 andthen to oil drain 28 through check valve 72 into the cyclone 61 anddownwards along the sides of the cyclone 61. Additionally, oil which isalready separated from the blow-by gas within regulator 8 can also flowto oil sump 70. Oil from drain 28 is returned to the crankcase.

The separator 10 may be considered to be a variable impactor separatoras it is intended to respond to differences between the blow-by gasinlet pressure and the outlet pressure to increase the separationefficiency, as will now be described with reference to FIG. 3.

Contaminated engine crankcase blow-by gases enter the separator inlettube 60 along the path of arrow 62. The upper end of inlet tube 60 isseparated from an annular impaction chamber 80 by diaphragm 64.Diaphragm 64 may form a radial seal with the upper end of tube 60 as itmoves towards or away from the upper end of tube 60 or the diaphragm 64may be arranged to never fully make contact with tube 60. Diaphragm 64also separates the inside of tube 60 from chamber 82. Chamber 82 is keptat atmospheric pressure by an air inlet (not shown) which connects tothe outside of the CCV system. The inside of tube 60 is at substantiallythe same pressure as the engine crankcase, allowing for any differencein pressure across regulator 8.

Blow-by gas passes into the impaction chamber 80 through one or morevertical slots 66 which are open at the upper end of the tube. The formof slots 66 can be more clearly understood through the perspective viewof FIG. 4. The size and number of slots 66 determines the minimumdifferential pressure drop across the variable impactor separatorsystem. This pressure drop is directly related to the separationefficiency of the CCV system. Impaction and separation of oil particlesdue to radial acceleration in making a 180° turn occurs both on thediaphragm face and the impaction surface 68. The impaction surface maybe covered with a material opposite the slots 66 to improve theco-efficient of restitution of oil droplets on the outer walls, ratherthan act as a pass through media. The media covering the impactionsurface serves to reduce re-entrainment of the contaminants. Oilseparated from the blow-by gas at the impaction surface 68 then flowsunder gravity to the oil sump 70 and ultimately to oil drain 28 asdescribed above.

The gas stream flows downwardly towards the sump after being deflectedby the impaction surface. It is then diverted to flow upwardly by meansof a baffle, as indicated in FIG. 2 by the arrow 56. The baffle is shownin FIG. 2 being inclined upwardly towards the outer wall of the filterwith a drain for oil at the inner edge of the baffle, close to the wallof the separator inlet tube 60. It can be preferable for the baffle tobe inclined downwardly towards the outer wall of the filter, with adrain for oil towards the outer edge of the baffle close to externalwall of the housing. In this way, the gas stream flowing over the bafflecan help to encourage oil on the surface of the baffle to flow outwardlytowards the drain, to drain into the sump.

The jet pump 12 connected downstream of impaction chamber 80 is used toovercome the pressure drop of the variable impactor separator. Theseparation performance achievable is therefore no longer limited as withconventional unpowered impactor systems. At the same time an acceptablecrankcase pressure close to atmospheric pressure can be maintained.

As the engine load, speed or engine braking conditions change both thevacuum generated by the jet pump 12, and the volume of blow-by gaspassing through the separator 10 change. To maintain an acceptablecrankcase pressure according to the variable vacuum conditions generatedby the jet pump 12, the diaphragm 64 is allowed to open and close thegap between the top of the tube 60 and the diaphragm 64 above the openends of the slots 66. The chamber 82 is kept at atmospheric pressuresuch that any net positive pressure on the diaphragm will cause it toopen creating or widening an annular gap above the end of tube 60, whichreduces the pressure drop across the separator 10. As soon as a netvacuum is generated by the jet pump the diaphragm fully closes (which asnoted above may cause the diaphragm 64 to contact the top of the tube,or a gap may be preserved), ensuring that the separator 10 is operatingat maximum separation efficiency. The pressure differential of theseparator 10 is adjusted and crankcase pressure can be regulatedprecisely according to the specification of the regulation spring 84.Spring 84 extends between supports 86 within tube 60 and the diaphragm64, to which it is attached at central part 88. Additionally a secondregulation spring may be provided in chamber 82 to act upon the oppositeside of diaphragm 64 to control positive pressures.

The CCV system described above in accordance with FIGS. 2 to 4incorporates a pressure regulator 8 arranged to control the crankcasepressure and an impactor separator 10. Alternatively, the separator 10may be provided with one or more slots 66 which are shaped to provide anappropriate variation in open cross sectional area according to thepressure differential between the blow-by gas pressure and atmosphericpressure, which is achieved by having a slot with a specifically chosencross sectional area. This may in addition to, or as a completereplacement to, the pressure regulator 8. A separator 10 incorporatingsuch a variable slot is shown in FIG. 5.

FIG. 5 shows a separator 10 incorporating the function of an antipump-surge regulator within a variable impactor separator. The diaphragm64 comprises a rolling diaphragm, which is used to precisely adjust theaperture of a variable slot profile to regulate crankcase pressure andcontrol the phenomenon of pump surge. Specifically, the diaphragm 64comprises a central portion 100 arranged to couple to regulator spring84. As for the embodiment of FIGS. 2 and 3 there may be a secondregulator spring within atmospheric reference chamber 80. The diaphragm64 further comprises an annular rolling portion 102, alternativelyreferred to as a rolling convolute, which progressively covers anduncovers slot 66 as the central portion 100 moves up and down. As inFIG. 2, the separator of FIG. 5 incorporates a pre-cyclone separator 61which separates out a portion of the contaminants within the blow-by gasbefore it reaches the variable impactor separator. As for the separatorof FIG. 2, the blow-by gas enters the cyclone 61 via an inlet towardsone side of the cyclone 61 and the separator inlet tube 60 projectsdownwards into the cyclone 61 to serve as a cyclone vortex finder suchthat the blow-by gas flows to inlet tube 60 generally along the path ofarrow 62.

The rolling diaphragm 64 can be used to optimise the performance of theimpactor separator 10 according to the available vacuum pressure frompump 12. As the available vacuum increases, the diaphragm 12 closes,thus increasing velocity, separation performance and pressuredifferential across the impactor 10 until atmospheric pressure isequalised by the inlet pressure to the separator. Slot 66 generallycomprises a tapering slot, which may be curved as shown. Towards thediaphragm 64, slot 66 broadens significantly so as to provide for alarge flow of blow-by gas in the event of a reduction in the availablevacuum from pump 12, thereby preventing the crankcase pressure risingunacceptably.

FIG. 6 shows the diaphragm 64 in a generally closed position, althoughit will be appreciated that the diaphragm may move further downwards.Only the bottom, narrow portion of the slot is exposed and available forgas to flow through. In FIG. 7 the diaphragm 64 in an almost fully openposition, although it will be appreciated that the diaphragm may movefurther upwards. A greater proportion of the slot is exposed, includingthe broader upper part, and available for gas to flow through. Whenfully uncovered the slot 66 can be seen to have a narrow, tapering lowerpart and a significantly broader upper part. The narrow portion of slot66 is intended to produce the precise pressure control function requiredto counter pump-surge conditions. When the diaphragm 64 is lowered, theminimal open area gives a high pressure differential across theseparator 10 and optimal impactor performance for the available pumpvacuum. When the diaphragm 64 is raised, the large upper area of slot 66is matched to regulate crankcase pressure under high flow conditions,such as may be experienced in a worn engine or under engine braking. Thediaphragm may be arranged to fully cover the slot 66 at the furthestextent of its downward movement, or to ensure that at least part of theslot remains open. Adjustment of the response of the or each spring andadjustment of the relative sizes of the first and second sides of thediaphragm 64 acted upon by the blow-by gas, the ambient gas pressure andthe pump vacuum can be used to control the rate and extent of movementof diaphragm 64.

Slot 66 comprises a variable section impactor slot. The varying openarea of slot 66 exposed by the diaphragm as it moves has benefits bothin terms of the separation of particles from the blow-by gas stream andalso for control of crank case pressure. The blow-by gas stream includesa range of particle sizes travelling at the same velocity but havingdifferent momentums due to their different sizes and masses. Heavyparticles with a high momentum exit towards the top of the tube throughthe wider part of the slot. Lighter particles exit the tube lower downthe slot. As the slot is smaller at the bottom, lighter particles areaccelerated to a higher velocity, thereby increasing their momentum.Advantageously, this reduces the difference in momentum between smalland large particles which allows for a reduction in the difference inseparation efficiency between small and large particles withoutrestricting the aperture size (which would cause an increase incrankcase pressure).

Furthermore, the variable section impactor slot improves the pressurecontrol across the separator. When the diaphragm is raised and the wideupper section of the slot is exposed, this allows for a large aperturesize which is able to accommodate high volume blow-by gas conditionswhile maintaining the pressure differential across the separator (andhence the inlet pressure of the blow-by gas and the crankcase pressure)within acceptable limits. When the diaphragm lowers under low flowconditions, the decreased open area of the lower section of the slotincreases the pressure differential across the separator, therebypreventing negative pressures being generated in the crankcase (relativeto atmospheric pressure). The changing cross-sectional area of theaperture provides a non-linear pressure differential response for alinear movement of the diaphragm, which allows for improved, andcontrollable, regulation of the pressure differential across theseparator.

Movement of the diaphragm 64 ensures that the available pressure dropprovided by the pump is used efficiently to achieve contaminantseparation without causing the crankcase pressure to fall belowpredetermined limits. This is an improvement over the separator of FIG.3 for which the open area of the aperture does not change as rapidly.The effect for the separator of FIG. 3 is that a portion of the vacuumgenerated by the pump purges through the aperture, which requires aseparate regulator to control the crankcase pressure. The improvement inpressure control provided by the separator of FIGS. 5 to 7 allows theseparate pressure regulator at the blow-by gas inlet to the CCV systemto be omitted in certain embodiments. It will be appreciated that theprecise shape of the slot may vary widely. For instance, the slot may behelical extending around the tube 80. The helical slot may be generallyconstant width over at least part of its length before tapering at itsclosed end in order to provide an appropriate non-linear response in thecross-sectional area of the aperture for a given movement of thediaphragm. In alternative embodiments in place of one or more slotsextending upwards along the tube there may be a number of separateclosed apertures through the wall of the tube that are covered oruncovered by the diaphragm. For instance, in place of a helical slotthere may be a line of apertures arranged along a helix. The size of theapertures may vary along the length of the helix.

The diaphragm 64 comprises an actuator arranged to control the flow ofblow-by gas through slot 66. Slot 66 is cut into the tubular wall 60.The slot 66, in combination with the tubular structure 60 defines anopen area through which blow-by gas can flow. The shape of the slot 66is arranged to ensure that the pressure differential across the slot isappropriate for the flow-rate and vacuum characteristics generated bythe pump. By controlling the shape of slot 66 a linear or non linearrelationship between any change in pump vacuum, atmospheric pressure andcrankcase pressure and the corresponding distance travelled by thediaphragm can be achieved. More specifically, the shape of the slot 66can be chosen such that movement of the diaphragm 64 at a constant ratecauses a non-linear response in the open area of the slot. Effectivelyany closed loop control function can be generated by the diaphragm 64 inresponse to a given input from the pump. More accurate crankcasepressure regulation can be achieved than for conventional arrangementsof separators and regulators. Moreover, because regulation of thecrankcase pressure is combined with the separator there may be no needto provide an additional pressure regulator. The separation efficiencyis increased by accurately controlling the flow of the blow-by gas.

It can be seen that for the slot 66 of FIG. 5, as diaphragm 64 movesdownwards, the rate of reduction of the open area of the slot increases.This is because the slot 66 tapers towards its closed end. Movement ofdiaphragm 64 may be limited to ensure that the open area is nevercompletely closed off

It will be readily apparent to the appropriately skilled person that theshape of the slot 66 may vary significantly in order to achieve thedesired closed loop control function. For instance, the slot may broadentowards its closed end, be of constant width or initially taper andterminate with an enlarged portion to prevent full closure of the openarea. Furthermore, multiple slots of different sizes and shapes may beprovided around the tubular wall. It will be further apparent that theway in which movement of the diaphragm 64 covers and uncovers the slotmay vary, and alternatives to the rolling convolute will be apparent tothe skilled person and fall within the scope of certain of the appendedclaims. Where the claims of the present invention specify variableimpactor separation stages this should be considered to cover anyvariable separator incorporating a regulator in which a first chamberand a second chamber are coupled together by one or more slots and theopen area of the or each slot is arranged to be varied according to theposition of a diaphragm or other moveable actuator which adjusts itsposition according to a pressure differential between gas in the firstand/or second chambers and an external pressure reference.

Variable separators have been primarily described herein in use as partof a CCV system. However, it will be readily apparent to theappropriately skilled person that they may be more widely applicable.More generally, such a separator may be used in any application in whichit is necessary to filter contaminants from a fluid stream and desirableto regulate a pressure drop for a fluid between a first chamber and asecond chamber, with reference to an external pressure. Typically, thefluid will be a gas. Separators according to the present invention areof particular benefit in pumped systems in order to obviate or mitigatethe effects of pump surge and pressure hunting described above.

Separators as described above have been observed to provide gravimetricseparation efficiency in the range 95-98%. Such separators may beadapted to filter contaminants from blow-by gas in a closed loop systemtypically operating with a flow of blow-by gas of 50-1500 l/min. Theflow of boost gas through nozzle 52 when using boost gas derived fromthe turbocharger of an engine typically comprises less than 1% of thetotal engine gas flow, so as to have a negligible effect on engineperformance.

The inventors of the present application have identified that it ispossible to obtain further improvements in the separation efficiency byusing multiple separation stages in which at least one separation stagecomprises a variable impactor separator as described above incombination with a pump. It is known that for separators without anexternal source of energy in the form of a pump there is no significantincrease in separation efficiency by coupling together separators inseries. However, it has been identified by the inventors of the presentinvention that by providing a pump, for instance a jet pump, to drawblow-by gas through the separator it is possible to use multipleseparation stages to increase the gravimetric separation efficiency to arequired level to meet the challenge posed by stringent emissionslegislation while simultaneously minimising pump power consumption.Multiple powered variable impactor separators coupled together inseries, or a powered variable impactor separator in series with a filtermedia can be specifically designed to yield higher gravimetricefficiency than a single stage variable impactor separator driven by apump of the same power, while maintaining crankcase pressure withinacceptable limits. Without the additional motive power provided by apump it has been found that the a series of impactors coupled in seriesare unable to yield the required improvement in gravimetric separationefficiency when applied to the separation of diesel engine blow-byaerosols. The application of a pump allows the fractional separationefficiency of each separation stage to be optimised to the specifics ofan engine's aerosol challenge distribution to bring about an overallimprovement in gravimetric separation efficiency.

The fractional separation efficiency of a separator is the separationefficiency measured as a function of particle size. For a multi-stageseparator the required fractional separation efficiency for eachseparation stage can be compared with the equivalent fractionalseparation efficiency of a single stage impactor to achieve the samegravimetric efficiency for a particular particle challenge distribution(that is for a given distribution of particle sizes in the blow-by gas).For a pumped separator providing an overall differential of, forinstance, 100 mBar the required fractional separation efficiency to meetthe particle challenge posed by the blow-by gas for a single 100 mBarvariable impactor of the type illustrated above can be calculated. Therequired fractional separation efficiency for two 50 mBar variableimpactor separators coupled in series can be calculated. The presentinventors have identified that the required fractional separationefficiency for each 50 mBar variable impactor separator is comparablewith or lower than the fractional separation efficiency which has beenmeasured for a 50 mBar variable impactor separator constructed inaccordance with FIGS. 2 to 7 described above. That is, by splitting theavailable pressure differential available from the pump across twoseparation stages instead of a single separator the gravimetricseparation efficiency may be improved, for instance from 95% to over99%. Dependent upon the prevailing engine conditions (including thevolume of blow-by gas produced and the composition of contaminantswithin the blow-by gas) the gravimetric separation efficiency mayapproach 100%. This significant, and hitherto unidentified, resultallows for yet higher fractional separation efficiencies and overallgravimetric efficiencies to be achieved using that same techniques forconstructing variable impactor separators described above. A moredetailed mathematical explanation of how a multi-stage separator canprovide this improvement is given below in connection with FIGS. 10 to15.

In accordance with embodiments of the present invention a variableimpactor separator as illustrated in FIGS. 2 to 7 may be combined with asecond separation stage (and optionally more than one additionalseparation stage). The second separation stage may be a second similarvariable impactor separator, as illustrated in FIG. 8. Alternatively,the second separation stage may be a media separator as illustrated inFIG. 9. In either scenario the two or more stage separator may alsoincorporate a pre-cyclone of the sort illustrated in FIGS. 2 and 5.

Referring to FIG. 8, this illustrates a separator in accordance with afirst embodiment of the invention. The separator comprises a cyclonicpre-filter 200, a first variable impactor separation stage 202 and aneductor pump 204 each of which is generally the same as the cyclonicpre-filter 61, separator 10 and jet pump 12 of FIG. 5 and so will not befully described again here. However, differing from the separator ofFIG. 5, between the first variable impactor separation stage 202 and thejet pump 204 is a second variable impactor separation stage 206. Thesecond variable impactor separation stage 206 which is generally thesame as the first variable impactor separation stage 202, however it maybe optimised to further increase the overall fractional and gravimetricseparation efficiencies by the use of springs having different springresponse rates. In particular, the spring response rate for the springsin the second stage 206 may be chosen to allow a portion of the vacuumgenerated by the jet pump 204 to purge through the second stage 206 toallow the split of the available pressure differential generated by thevacuum between the two separation stages to be fine tuned to adjust thefractional separation efficiency of each separation stage in order tooptimise the overall gravimetric separation efficiency. Blow-by gas isdrawn through the separator by the jet pump 204 such that the blow-bygas passes from inlet 208 sequentially through the cyclonic pre-filter200 and the first and second variable impactor stages 202, 206 beforebeing discharged through gas outlet 210.

As for the separator of FIG. 5, each variable impactor separator stage202, 206 incorporates the function of an anti pump-surge regulatorwithin an impactor separator. Each separator stage 202, 206 isfunctionally equivalent to the separator of FIG. 5, being based upon arolling diaphragm 212, which is used to precisely adjust the aperture ofa variable slot profile to regulate crankcase pressure and maximiseseparation efficiency according to the available vacuum pressure frompump 204 to vary the open area of an aperture between the inside of tube214 and the annular chamber surrounding tube 214. The diaphragm 212continually matches the impactor pressure drop to the transient vacuumconditions generated by the jet pump 204. However, the shape of the slot216, which in combination with the diaphragm 212 defines the aperturefor each separation stage, differs from that shown in FIG. 5.Specifically, each slot 216 is helically wound around at least part oftube 214 such that movement of diaphragm 212 along the axis of tube 60results in a more rapid change in the open area of the aperture. As forthe slot 66 of FIG. 5, the slot 216 in each variable impactor separator202, 206 is preferably tapered towards its closed end to allow for anon-linear change in the open area of the aperture for a linear rate ofchange of the position of diaphragm 212 and a linear rate of change ofthe pressure differential across each diaphragm 212. This providessmooth crankcase pressure control and avoids pump surge and pressurehunting across the separator, particularly when a jet pump it used. Afurther advantage is that because crankcase pressure regulation isintegrated into the separator, it is not necessary to provide a separateregulator component.

The shape of each slot 212 is arranged to provide an appropriateresponse to changes in inlet and outlet pressure across each separationstage. It will be appreciated that shape of the slots 216 may differbetween the two separation stages 202, 206. The shape of the slots 216may vary widely from those shown in FIGS. 5 to 8. Furthermore, thespring response rate of the or each spring and adjustment of therelative sizes of the first and second sides of the diaphragms 212 actedupon by the blow-by gas and the ambient gas pressure can be used toseparately control the rate and extent of movement of each diaphragm212.

The variable impactor separator slots 216 improve the pressure controlacross each separation stage 202, 206. When the diaphragms 212 areraised and the size of the apertures increases, this allows for a largeaperture size which is able to accommodate high volume blow-by gasconditions while maintaining the pressure differential across theseparator (and hence the inlet pressure of the blow-by gas and thecrankcase pressure) within acceptable limits. When the diaphragms lower,the decreased open area of the lower section of the slots increases thepressure differential across the separator, thereby preventing negativepressures being generated in the crankcase (relative to atmosphericpressure). The changing cross-sectional area of the aperture can beused, if required, to provide a non-linear pressure differentialresponse for a linear movement of the diaphragm, which allows forimproved, and controllable, regulation of the pressure differentialacross the separator. The improvement in pressure differential allowsthe separate pressure regulator at the blow-by gas inlet to the CCVsystem to be omitted in certain embodiments of the present invention.

Advantageously, the use of a pump such as the jet pump 204 illustratedin FIG. 8 raises the fractional efficiency of each stage of a multi-passimpaction separator to a level at which there is an overall improvementin gravimetric efficiency. Furthermore, by appropriate control of eachseparation stage the fractional separation efficiency of the separatorcan be tailored to the specific oil particle size distribution withinthe blow-by gas received from any given engine.

Blow-by gas passes through the separator of FIG. 8 as follows: Blow bygas enters through inlet 208, which is coupled to the crankcase of theengine. The gas passes into the cyclonic pre-filter 200 along the pathof arrow 230 where it forms a cyclone spiralling about the vortex finder232 which forms the base of the inlet tube 214 of the first variableimpactor separation stage 202. A proportion of the contaminants are shedupon the wall of the cyclonic pre-filter 200 and flows downwards to oildrain 234 as the gas flows upwards through inlet tube 214 along the pathof arrow 236. The blow-by gas passes through each variable impactorseparation stage 202, 206 in the same way as described above inconnection with FIGS. 5 to 7 passing upwards through the inlet tube 214,through slot 216 and back down through the annular chamber surroundingthe inlet tube 214 and defined by a concentric outer tube generallyalong the path of arrow 238. Separation of oil and other contaminantsoccurs as the gas is accelerated through slot 216 and impacts against animpaction surface formed within the annular chamber. A coalescing mediamay be provided on the impaction surface to reduce the rate ofre-entrainment of contaminants. The coalescing media reduces thetendency of particulate contaminants to bounce off the impactionsurface.

The open area of each slot 216 is determined by the position of eachdiaphragm 212 according the differential pressure across the diaphragmbetween the inside of tube 214 and the pressure reference in chamber240. Each chamber 240 may be coupled to the ambient environment or maybe coupled to any other reference gas pressure. Additionally movement ofthe diaphragms 212 is controlled by the spring response rates of springs242, which may differ from one another. Springs may also be providedcoupled to the diaphragm within chamber 240 in addition to springs 242or in place of springs 242. In some embodiments no springs are requiredat all. Oil separated from the blow-by gas flows downwards and passesthrough check valves 244 towards the oil drain 234. The cleaned gas isdirected upwards generally along the path of arrow 246 from the firstseparation stage 202 to the second separation stage 206. After thesecond separation stage 206 the clean gas is directed upwards generallyalong the path of arrow 248 to the jet pump 204 where it is acceleratedby the boost gas which enters the jet pump 204 through nozzle 250. Theboost gas and the cleaned blow by gas exit the jet pump 204 throughdiffuser tube 252.

As noted above, the multi-stage separator of FIG. 8 also includes acyclonic pre-filter 200, however it will be understood that inalternative embodiments this may be omitted. Additionally, while theseparator of FIG. 8 incorporates two variable impactor separator stagesproviding inertial impaction, it will be appreciated that furthervariable impactor separator stages may be provided with each stageoperating within a proportion of the overall pressure differentialacross the separator provided by the jet pump.

Referring to FIG. 9, this illustrates a separator in accordance with asecond embodiment of the present invention. The separator is generallythe same as that shown in FIG. 8 except that the second variableimpactor separator stage 206 has been replaced by a filter mediaseparation stage 218. This combination of inertial impaction within thevariable impactor separator 202 (and also within the cyclonic pre-filterif present) followed by fibrous depth filtration has shown to provideexceedingly high fractional and gravimetric efficiencies. In particular,certain types of known filter media are particularly suitable forfiltering very small particle contaminants. As the filter media is notclogged by larger particles due to the action of the variable impactorseparator, the filter media is better able to retain this ability tofilter very small particles. Additionally, unlike certain conventionalfilters in which a filter media is provided on its own and must beregularly replaced, because the variable impactor separator 202 removesa large proportion of the contaminants within the blow-by gas the filtermedia 220 within filter media stage 218 has an extended service life.Typically media elements will block with soot and particulates dependanton the size and density of the media and soot concentration of theblow-by gas. Where typically depth filtration have service intervalsbetween 500 & 2000 hours, the filter media 220 within the separator ofFIG. 9 can have an increased service life of between 2000 and 12,000hours, and may even be serviceable for the life of the engine.

The flow path of blow-by gas through the separator of FIG. 9 isgenerally the same as that for the separator of FIG. 8 except that afterexiting the first separation stage 202 partially cleaned blow-by gas isdirected along the path of arrow 246 to the inside of the filter media220. The gas passes through the filter media 220 and then is directed tothe jet pump 204 as before. Due to the high separation efficiency of thefirst separation stage 202 (up to 95%) the filter media 220 may have aserviceable life of over 12000 hours for blow-by gas with a 1% sootcontaminant rate. In a further alternative the cyclonic pre-filter maybe omitted from both FIG. 8 and FIG. 9.

A more detailed mathematical explanation of how a multi-stage separatorcan provide an improvement in gravimetric separation efficiency will nowbe provided in connection with FIGS. 10 to 16. The present inventorshave developed techniques for identifying the minimum fractionalefficiency curve required for each component of a multi-stage separatorto yield a gravimetric separation efficiency which equals or exceeds thegravimetric efficiency of a comparable single stage device. Using thecalculated target fractional efficiency curve the fractional efficiencycurves for each stage can be manipulated by control of the differentialpressure available from the pump across each stage to fine tune theoverall gravimetric efficiency. This understanding can be used todetermine the optimal number of separation stages to maximise efficiencyfor any available vacuum, or to determine the required vacuum (andtherefore determine the required pump) and number of stages to meet agiven efficiency target. In this way the pump energy requirements tomeet a separation target can be minimised.

The performance of a device used for the cleaning of blow-by gasesemitted from an engine can be evaluated by collecting the contaminantscontained before and after the separator on filter papers over a fixedtime period and weighing them in order to calculate a gravimetricseparation efficiency.

The gravimetric efficiency of a multi-pass separator can be calculatedreadily. For example, a second pass through a 50% efficient separator(for any type of inertial separator) will remove a further 50% of thecontaminant mass carried over from the first pass. The overallefficiency of the two pass system is therefore 75%. A third pass willyield 88% overall and the fourth 94% etc. For any given efficiency (x,between 0% and 100%) for a single separator stage a mathematicalequation can be derived for the overall efficiency of a multi-stageseparator (μ_(n) where n is the number of similar separator stages inthe multi-stage separator):

$\mu_{2} = {\left\lbrack {1 - \left\lbrack {\left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right)} \right\rbrack} \right\rbrack \cdot 100}$$\mu_{3} = {\left\lbrack {1 - \left\lbrack {\left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right)} \right\rbrack} \right\rbrack \cdot 100}$$\mu_{4} = {\left\lbrack {1 - \left\lbrack {\left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right) \cdot \left( {1 - \frac{x}{100}} \right)} \right\rbrack} \right\rbrack \cdot 100}$

These equations can be simplified as follows:

$\mu_{2} = {- \frac{x \cdot \left( {x - 200} \right)}{100}}$$\mu_{3} = \frac{x \cdot \left( {x^{2} - {300 \cdot x} + 30000} \right)}{10000}$$\mu_{4} = {\frac{x^{3}}{2500} - \frac{x^{4}}{1000000} - \frac{3 \cdot x^{2}}{50} + {4 \cdot x}}$

A graph of the functions above for second, third and fourth passseparators is shown in FIG. 10, which can be used to determine thesystem efficiency for second, third or fourth pass separators of anygiven efficiency x. It can be seen that regardless of the number ofseparator stages, the overall efficiency μ approaches 100% as theefficiency of each one of the stages x approaches 100%.

It will be understood by the person skilled in the art that an inertialseparator having an acceptable pressure differential of for example 40mbar may exhibit a gravimetric efficiency of approximately 75%. It willalso be understood that an inertial separator having a lower pressuredifferential of 20 mbar will typically yield a lower gravimetricseparation efficiency of approximately 44%. Two such separators coupledin series will possess a combined pressure differential of 40 mbar, yetusing the graph above it may be determined that the combined multi-stageseparator will yield a lesser gravimetric efficiency overall of only69%. It may be readily deduced that further dividing the availablepressure differentials across additional separator stages will deliverincreasingly poor results.

As discussed above and described in WO-2009/037496-A2 in the name ParkerHannifin (UK) Ltd, the present inventors have previously developed adevice for separating contaminants to an increased level of efficiencyby utilizing a pump to artificially increase the pressure differentialavailable for achieving performance improvements. The present inventorshave now developed a method for achieving the more efficient use of pumpenergy for a given aerosol challenge posed by blow-by gas from an engineby the application of multi-pass separation as will now be described.

The composition of engine blow-by gases comprises both liquid oil andoil aerosols ranging in size from 0.035 microns to 10 microns. Usingexisting equipment the characteristic mass fractions produced by anindividual engine may be measured. An example is shown in FIG. 11 for a2010 diesel engine in which the proportional make up of the blow-by gasis plotted against particle size in μm. FIG. 11 shows a significantconcentration of contaminants between approximately 0.2 μm and 1.5 μmand above 5 μm.

Similarly, using the same existing equipment the separation efficiencyof a variable impactor separator of the type generally described abovein connection with FIGS. 5 to 7 can be plotted over the same range ofparticle sizes. The fractional separation efficiencies of such variableimpactor separators have been characterised over a range of pumpedpressure differentials and this data is shown in FIG. 12. It can be seenthat increasing the pressure differential raises the fractionalseparation efficiency curve.

In order to maximise the gravimetric separation efficiency whilesimultaneously minimising the pump energy it is necessary to tailor amulti-stage separator to achieve the highest possible efficiency atspecific particle sizes corresponding to significant oil mass fractionsgenerated by a given engine. The pressure differential across eachseparator stage can be chosen to tune each stage to separate particlesfrom a chosen part of the aerosol challenge illustrated in FIG. 11. Tomaximise overall gravimetric separation efficiency it is not sufficientto simply couple multiple separators in series, with or without thepower provided by a pump.

A mathematical function defining the minimum fractional efficiency curverequired for each separator stage in order for a multi-pass system toyield equal performance to that measured from of a single pass separatorcan be determined. Re-arranging the previous equations for second, thirdand fourth pass systems in terms of x achieves this. Note that thesecond, third and fourth pass equations are second third and fourthorder polynomials and therefore have multiple solutions:

For a two stage separator:

$\quad\begin{pmatrix}{{50 \cdot \sqrt{4 - \frac{\mu_{2}}{25}}} + 100} \\{100 - {50 \cdot \sqrt{4 - \frac{\mu_{2}}{25}}}}\end{pmatrix}$

For a three stage separator:

$\quad\begin{bmatrix}{{\left( {{10000\;\mu_{3}} - 1000000} \right)^{\frac{1}{3}} + 100}\;} \\{\frac{\sqrt{3} \cdot \left( {{10000\;\mu_{3}} - 1000000} \right)^{\frac{1}{3}} \cdot i}{2} - \frac{\left( {{10000\;\mu_{3}} - 1000000} \right)^{\frac{1}{3}}}{2} + 100} \\{100 - \frac{\left( {{10000\;\mu_{3}} - 1000000} \right)^{\frac{1}{3}}}{2} - \frac{\sqrt{3} \cdot \left( {{10000\;\mu_{3}} - 1000000} \right)^{\frac{1}{3}} \cdot i}{2}}\end{bmatrix}$

For a four stage separator:

$\quad\begin{bmatrix}{{500 \cdot \sqrt{2} \cdot \left( {\frac{1}{2500} - \frac{\mu_{4}}{250000}} \right)^{\frac{1}{4}}} + 100} \\{100 - {500 \cdot \sqrt{2} \cdot \left( {\frac{1}{2500} - \frac{\mu_{4}}{250000}} \right)^{\frac{1}{4}}}} \\{{500 \cdot \sqrt{2} \cdot \sqrt{- \sqrt{\frac{1}{2500} - {\frac{1}{250000} \cdot \mu_{4}}}}} + 100} \\{100 - {500 \cdot \sqrt{2} \cdot \sqrt{- \sqrt{\frac{1}{2500} - {\frac{1}{250000} \cdot \mu_{4}}}}}}\end{bmatrix}$

μ₂, μ₃ and μ₄ vary between 0 and 100%. Simplifying these equationsfurther yields:

$\left. {{\left. {{{f\left( {\mu\; 2} \right)}:={100 - {50 \cdot \sqrt{4 - \frac{\mu\; 2}{25}}}}}{\mu\; 3}} \right):={\left( {{{10000 \cdot \mu}\; 3} - 1000000} \right)^{\frac{1}{3}} + 100}}{\mu\; 4}} \right):={100 - {500 \cdot \sqrt{2} \cdot \left( {\frac{1}{2500} - \frac{\mu\; 4}{250000}} \right)^{\frac{1}{4}}}}$

From this, in order to design a multi-pass separator system capable ofyielding higher gravimetric separation efficiency than a known singlepass device of equal total pressure differential, the minimum requiredfractional separation efficiency at each particle size in the region ofinterest for the aerosol challenge shown in FIG. 11 can be calculated.FIG. 13 shows the fractional separation efficiency for a single variableimpactor separator having a pressure differential of 120 mBar, therequired target fractional separation efficiency for each of two 60 mBarvariable impactor separators and the measured fractional separationefficiency for an exemplary 60 mBar variable impactor separator. It canbe seen that the performance of the exemplary 60 mBar separator exceedsthe required performance of each stage of the multi-stage system. Anydevice above the derived target curve will yield on overall improvementin gravimetric efficiency, while any device below it will not.Consequently FIG. 13 shows that according to the mathematical modeldeveloped by the present inventors two 60 mbar variable impactorseparators in series can yield higher efficiency than a single 120 mbarseparator. This result is confirmed in FIG. 14 which shows the measuredfractional separation efficiency for a single 60 mBar variable impactorseparator, a single 120 mBar variable impactor separator and two 60 mBarvariable impactor separators coupled in series. The performance of thetwo 60 mBar separators coupled in series exceeds the performance of thesingle 120 mBar separator through out the particle size region ofinterest.

Using the above described techniques, the skilled person will understandhow a multi-pass variable impactor separator of the type illustrated inFIG. 8 can be specifically designed to deliver previously unattainedgravimetric efficiencies when challenged by a characterised engineblow-by gas aerosol distribution. FIG. 15 illustrates the fractionalseparation efficiency for a single 50 mBar separator, a single 100 mBarseparator and two 50 mbar separators in series. It can be seen that theperformance of the two 50 mBar separators in series is not uniformlyhigher than the performance of the single 100 mBar separator, but ishigher in the particular region of interest shown in FIG. 11 forparticles larger than 0.2 μm. This example shows how such a multi-stagevariable impactor separator would yield an overall system improvement ifthe greater portion of engine challenge mass fractions is above 0.2microns, while a loss in performance will result when challenge massfractions are below 0.2 microns. This illustrates the importance ofconsidering the particular aerosol challenge to be addressed whendesigning a multi-stage separator. Simply coupling previously availableseparators in series is no guarantee of a performance increase, unlessthere is also a significant increase in pump energy. Without this fullunderstanding of the process behind separation in a multi-stageseparator and how this may be tuned to a particular fluid to beseparated there would be nothing to suggest to the skilled personmodifying an existing separator by the addition of a further separationstage as to do so would be likely to lead to no significant improvement.

Similarly the performance of a powered multi-stage separator of the typeillustrated in FIG. 9, comprising a variable impactor inertial separatorand a pass through filter media, can be modelled. FIG. 16 illustratesthe fractional separation efficiency of an unpowered variable impactorseparator, a pump assisted variable impactor separator, a low densityfilter media and the combination of a pump assisted variable impactorseparator and a low density filter media coupled together in series. Oneskilled in the art of fluid separation will understand that the midrange dip in the fractional efficiency for the filter media around 0.35μm is due to the physics of the inherent impaction, interception anddiffusion separation mechanisms within the filter media. However, FIG.16 illustrates the known property of such filter medias to achieve highefficiency for particle sizes below 0.1 μm.

It will be appreciate from FIG. 16 that the combination of an unpoweredimpactor and a filter media would yield little improvement, beyondextending the service life of the filter media. However, following theunderstanding of how gravimetric separation efficiency can be improvedby tailoring the fractional separation efficiency of each stage of amulti-stage separator to a particular aerosol challenge, the presentinventors have identified that a combined system including a filtermedia and a powered impactor separator may provide significantlyimproved gravimetric separation efficiency. The combined system benefitsfrom the strengths of each stage, by tuning the fractional efficiency ofthe variable impactor separator, to yield a gravimetric result of around99% or higher for blow-by gas—levels of separation efficiency which havepreviously unachievable in the industry.

The separator may typically be made from a polymeric material, forexample glass filled nylon. Other constructions and materials will bereadily apparent to the appropriately skilled person. For example, thepump nozzle may be made from a sintered or metal injection moulded part.The various parts of the separator may be joined together usingappropriated fixing techniques, which will be well known to the skilledperson, such as clips, bolts, adhesive or welding. Seals such as O-ringsmay be provided to prevent leakage from the separator. The various partsof the separator may be provided in a modular system in which additionalstages may be incorporated or switched in order with minimalmodification.

Although the embodiments of the invention illustrated in FIGS. 8 and 9make use of a jet pump in order to increase the pressure differentialacross the multi-stage separator, the present invention is not limitedto this. Any known form of pump for generating a vacuum to draw blow-bygas through the separator may be used in order to allow multipleseparators to be used in series to provide higher overall gravimetricand fractional separation efficiencies. For instance, in certainembodiments of the invention an electrically or hydraulically drivenpump may be used.

While the embodiments of the invention illustrated in FIGS. 8 and 9 makereference to oil being drained from the separator and returned to thecrankcase, the oil and other contaminants may be stored outside of thecrankcase or disposed of Similarly, filtered blow-by gas is notnecessarily passed to the engine air intake, for instance it may bedischarged to atmosphere to avoid any residual contamination damagingthe engine, or may be processed by the exhaust system. In a furthermodification, the boost gas may be derived any source of pressurisedgas, for instance exhaust gas, compressed gas from a turbocharger or anengine intake manifold, compressed gas from a vehicle braking system orother sources. Other possible configurations will be readily apparent tothe appropriately skilled person.

Although particular separators described above relate primarily to theuse of the described separator for separating particulate and liquidaerosol contaminants from a blow-by gas stream within a reciprocatingengine, the present invention is not limited to this. Indeed, theseparator can be used to separate contaminants from a gas stream derivedfrom other forms of internal combustion engine. More generally, thepresent invention can be applied to separate contaminants from any gasstream, such as compressed air lines, separating cutting fluid from gasstreams in machine tools and separating oil mist in industrial aircompressors. More generally still, the present invention can be used toseparate contaminants from any fluid stream. That is, it may also beapplied to liquid streams. The separator may be advantageously used toseparate contaminants from an oil or fuel supply within an internalcombustion engine.

The separator may comprise a stand alone device. Alternatively, it mayreadily be integrated into other engine components, for example anengine valve cover, timing cover, crankcase, cylinder head, engine blockor turbocharger. The separator may be mounted directly on the engine, ormounted away from the engine.

Further modifications and applications of the present invention will bereadily apparent to the appropriately skilled person, without departingfrom the scope of the appended claims.

What is claimed is:
 1. A separator for separating contaminants from afluid stream, the separator comprising: a. a first inlet to receive afirst fluid stream including entrained contaminants; b. first and secondvariable impactor separators which are fluidly coupled together inseries, with the first of the variable impactor separators fluidlycoupled to the first inlet to receive the first fluid stream from thefirst inlet and each arranged to separate contaminants from the firstfluid stream; and c. a pump fluidly coupled to the second variableimpactor separator to generate an area of reduced pressure to draw thefirst fluid stream through the first and second variable impactorseparators; d. wherein each of the variable impactor separatorscomprises: i. a first chamber to receive the first fluid stream; ii. asecond chamber fluidly coupled to the first chamber through at least oneaperture such that the first fluid stream is accelerated through theaperture and is incident upon an impaction surface in the second chamberin the path of the first fluid stream such that contaminants areseparated from the first fluid stream; and iii. an actuator to adjustthe open area of the at least one aperture according to a pressuredifferential between fluid pressure in the first chamber and a referencefluid pressure in a third chamber.
 2. A separator according to claim 1,wherein for each of the first and second variable impactor separators,the impaction surface is within the second chamber and is located todeflect the first fluid stream after the first fluid stream enters thesecond chamber such that contaminants are separated from the first fluidstream.
 3. A separator according to claim 1, wherein for each of thefirst and second variable impactor separators, the shape of the apertureis chosen such that the rate of change of the open area of the aperturehas a non-linear response to a change in the pressure differentialbetween the first and third chambers.
 4. A separator according to claim1, further including a drain arranged to allow liquid contaminants todrain from the first variable impactor separator.
 5. A separatoraccording to claim 1, wherein the pump comprises a fourth chamber havinga second inlet for receiving a second fluid stream into the fourthchamber, the second inlet including a convergent nozzle for acceleratingthe second fluid stream, and a third inlet for receiving the first fluidstream, the third inlet being arranged relative to the second inlet suchthat the second fluid stream can entrain and accelerate the first fluidstream.
 6. A separator according to claim 1, wherein the pump iselectrically or hydraulically driven.
 7. A separator according to claim1, wherein the second variable impactor separator is coupled between thefirst variable impactor separator and the pump, and includes a firstchamber to receive the first stream from the first variable impactorseparator, and a second chamber fluidly coupled to the first chamberthrough at least the aperture such that the first fluid stream isaccelerated through the aperture in the second variable impactorseparator and is incident upon an impaction surface in the secondchamber in the fluid path of the first fluid stream in the secondvariable impactor separator such that contaminants are separated fromthe first fluid stream in the second variable impactor separator; and asecond actuator to adjust the open area of the at least one aperture inthe second variable aperture separator according to a pressuredifferential between fluid pressure in the first chamber and a referencefluid pressure in a third chamber of the second variable impactorseparator.
 8. A separator according to claim 1, further comprising acyclonic separator coupled between the first inlet and the firstvariable impactor separator, the cyclonic separator being arranged tocause fluid received from the first inlet to accelerate through a spiralcourse to separate contaminants from the first fluid stream.
 9. Aseparator according to claim 8, wherein the first variable impactorseparator comprises a variable impactor separator and an inner tubedefining the first chamber of the variable impactor separator extendsdownwards into the cyclonic separator to form the vortex finder of thecyclonic separator.
 10. A separator according to claim 1, wherein eachof the variable impactor separators includes a drain valve, and a drainpath is defined from the variable impactor separator in the secondseparation stage through a first drain valve, then through the variableimpactor separator in the first separation stage through a second drainvalve, to a drain outlet.
 11. A separator according to claim 10, whereineach of the variable impactor separators includes a sump for collectingcontaminants, and the drain valve in each stage is located in arespective sump.
 12. A separator according to claim 1, wherein for eachof the first and second variable impactor separators, the actuatorcomprises a diaphragm separating the first chamber from the thirdchamber.
 13. A separator according to claim 12, wherein for each of thefirst and second variable impactor separators, the first chamber isdefined by an inner tube arranged to receive the first fluid stream at afirst end of the inner tube and the second chamber is defined by anouter tube surrounding the inner tube and surrounding the first chamber,the second end of the inner tube being closed by the diaphragm.
 14. Aseparator according to claim 13, wherein for each of the first andsecond variable impactor separators, the diaphragm is arranged to movealong a longitudinal axis of the tubes in response to a change in thepressure differential between the first chamber and the pressurereference.
 15. A separator according to claim 14, wherein for each ofthe first and second variable impactor separators, the aperturecomprises a slot through the inner tube wall and the diaphragm furthercomprises a flexible portion arranged to progressively cover and uncoverthe slot to vary the open size of the aperture as the diaphragm moves.16. A separator according to claim 13, wherein for each of the first andsecond variable impactor separators, the aperture comprises a slotthrough the inner tube wall and the diaphragm further comprises aflexible portion arranged to progressively cover and uncover the slot tovary the open size of the aperture as the diaphragm moves.
 17. Acrankcase ventilation system comprising: a blow-by gas duct arranged toreceive blow-by gas from a crankcase; and a separator according to claim1, wherein the first inlet is coupled to the blow-by gas duct.
 18. Acrankcase ventilation systems according to claim 17, wherein the pump isarranged to be coupled to an engine air inlet system, to a vehicleexhaust system or to discharge gases to the ambient environment.
 19. Aninternal combustion engine comprising a crankcase ventilation systemaccording to claim 18, wherein the pump comprises a fourth chamberhaving a second inlet for receiving a second fluid stream into thefourth chamber, the second inlet including a convergent nozzle foraccelerating the second fluid stream, and a third inlet for receivingthe first fluid stream, the third inlet being arranged relative to thesecond inlet such that the second fluid stream can entrain andaccelerate the first fluid stream, wherein the second inlet is arrangedto receive a pressurised gas stream derived from a turbocharger and theseparator is operable to separate crankcase oil from the blow-by gas.20. An internal combustion engine comprising a crankcase ventilationsystem according to claim 17, wherein the pump comprises a fourthchamber having a second inlet for receiving a second fluid stream intothe fourth chamber, the second inlet including a convergent nozzle foraccelerating the second fluid stream, and a third inlet for receivingthe first fluid stream, the third inlet being arranged relative to thesecond inlet such that the second fluid stream can entrain andaccelerate the first fluid stream, wherein the second inlet is arrangedto receive a pressurised gas stream derived from a turbocharger and theseparator is operable to separate crankcase oil from the blow-by gas.